Broccoli: The Bro Client Communications Library

This page documents Broccoli, the Bro client communications library. It allows you to create client sensors for the Bro intrusion detection system. Broccoli can speak a good subset of the Bro communication protocol, in particular, it can receive Bro IDs, send and receive Bro events, and send and receive event requests to/from peering Bros.


What is Broccoli?

Broccoli is the BRO Client COmmunications LIbrary. It allows you to write applications that speak the communication protocol of the Bro intrusion detection system.

Broccoli is free software under terms of the BSD license as given in the COPYING file distributed with its source code.

In this document, we assume that you are familiar with the basic concepts of Bro, so please first review the documentation/publications available from the Bro website if necessary.

Feedback, patches and bug reports are all welcome, please see for instructions on how to participate in the Bro community.

Why do I care?

Having a single IDS on your network is good, but things become a lot more interesting when you can communicate information among multiple vantage points in your network. Bro agents can communicate with other Bro agents, sending and receiving events and other state information. In the Bro context this is particularly interesting because it means that you can build sophisticated policy-controlled distributed event management systems.

Broccoli enters the picture when it comes to integrating components that are not Bro agents themselves. Broccoli lets you create applications that can speak the Bro communication protocol. You can compose, send, request, and receive events. You can register your own event handlers. You can talk to other Broccoli applications or Bro agents – Bro agents cannot tell whether they are talking to another Bro or a Broccoli application. Broccoli allows you to integrate applications of your choosing into a distributed policy-controlled event management system. Broccoli is intended to be portable: it should build on Linux, the BSDs, Solaris, and Windows (in the MinGW environment).

Unlike other distributed IDSs, Bro does not assume a strict sensor-manager hierarchy in the information flow. Instead, Bro agents can request delivery of arbitrary events from other instances. When an event is triggered in a Bro agent, it checks whether any connected agents have requested notification of this event, and sends a copy of the event, including the event arguments. Recall that in Bro, an event handler is essentially a function defined in the Bro language, and an event materializes through invocation of an event handler. Each remote agent can define its own event handlers.

Broccoli applications will typically do one or more of the following:

  • Configuration/Management Tasks: the Broccoli application is used to configure remotely running Bros without the need for a restart.
  • Interfacing with other Systems: the Broccoli application is used to convert Bro events to other alert/notice formats, or into syslogd entries.
  • Host-based Sensor Feeds into Bro: the Broccoli application reports events based on host-based activity generated in kernel space or user space applications.

Installing Broccoli

The installation process will hopefully be painless: Broccoli is installed from source using the usual ./configure <options> && make && make install routine after extraction of the tarball.

Some relevant configuration options to pass to configure are:

  • --prefix=<DIR>: sets the installation root to DIR. The default is to install below /usr/local.
  • --enable-debug: enables debugging output. Please refer to the Configuring Debugging Output section for details on configuring and using debugging output.
  • --with-configfile=<FILE>: use FILE as location of configuration file. See the section on Configuration Files for more on this.
  • --with-openssl=<DIR>: use the OpenSSL installation below DIR.

After installation, you’ll find the library in shared and static versions in <prefix>/lib, the header file for compilation in <prefix>/include.

Using Broccoli

Obtaining information about your build using broccoli-config

Similarly to many other software packages, the Broccoli distribution provides a script that you can use to obtain details about your Broccoli setup. The script currently provides the following flags:

  • --build prints the name of the machine the build was made on, when, and whether debugging support was enabled or not.
  • --prefix prints the directory in the filesystem below which Broccoli was installed.
  • --version prints the version of the distribution you have installed.
  • --libs prints the flags to pass to the linker in order to link in the Broccoli library.
  • --cflags prints the flags to pass to the compiler in order to properly include Broccoli’s header file.
  • --config prints the location of the system-wide config file your installation will use.

The --cflags and --libs flags are the suggested way of obtaining the necessary information for integrating Broccoli into your build environment. It is generally recommended to use broccoli-config for this purpose, rather than, say, develop new autoconf tests. If you use the autoconf/automake tools, we recommend something along the following lines for your configure script:

dnl ##################################################
dnl # Check for Broccoli
dnl ##################################################
    AC_HELP_STRING(\[--with-broccoli-config=FILE], \[Use given broccoli-config]),
    [ brocfg="$withval" ],
    [ AC_PATH_GENERIC(broccoli,,
        AC_MSG_ERROR(Cannot find Broccoli: Is broccoli-config in path? Use more fertilizer?)) ])

broccoli_libs=`$brocfg --libs`
broccoli_cflags=`$brocfg --cflags`

You can then use the compiler/linker flags in your by substituting in the values accordingly, which might look as follows:

CFLAGS = -W -Wall -g -DFOOBAR @broccoli_cflags@
LDFLAGS = -L/usr/lib/foobar @broccoli_libs@

Suggestions for instrumenting applications

Often you will want to make existing applications Bro-aware, that is, instrument them so that they can send and receive Bro events at appropriate moments in the execution flow. This will involve modifying an existing code tree, so care needs to be taken to avoid unwanted side effects. By protecting the instrumented code with #ifdef/#endif statements you can still build the original application, using the instrumented source tree. The broccoli-config script helps you in doing so because it already adds -DBROCCOLI to the compiler flags reported when run with the --cflags option:

> broccoli-config --cflags
-I/usr/local/include -I/usr/local/include -DBROCCOLI

So simply surround all inserted code with a preprocessor check for BROCCOLI and you will be able to build the original application as soon as BROCCOLI is not defined.

The Broccoli API

Time for some code. In the code snippets below we will introduce variables whenever context requires them and not necessarily when C requires them. In order to make the API known, include broccoli.h:

#include <broccoli.h>


Broccoli’s memory management philosophy:

Broccoli generally does not release objects you allocate. The approach taken is “you clean up what you allocate.”


Broccoli requires global initialization before most of its other functions can be used. Generally, the way to initialize Broccoli is as follows:


The argument to bro_init() provides optional initialization context, and may be kept NULL for normal use. If required, you may allocate a BroCtx structure locally, initialize it using bro_ctx_init(), fill in additional values as required and subsequently pass it to bro_init():

BroCtx ctx;
/* Make adjustments to the context structure as required...*/


The BroCtx structure currently contains a set of five different callback function pointers. These are required for thread-safe operation of OpenSSL (Broccoli itself is thread-safe). If you intend to use Broccoli in a multithreaded environment, you need to implement functions and register them via the BroCtx structure. The O’Reilly book “Network Security with OpenSSL” by Viega et al. shows how to implement these callbacks.


You must call bro_init() at the start of your application. Undefined behavior may result if you don’t.

Data types in Broccoli

Broccoli declares a number of data types in broccoli.h that you should know about. The more complex ones are kept opaque, while you do get access to the fields in the simpler ones. The full list is as follows:

  • Simple signed and unsigned types: int, uint, uint16, uint32, uint64 and uchar.

  • Connection handles: BroConn, kept opaque.

  • Bro events: BroEvent, kept opaque.

  • Buffer objects: BroBuf, kept opaque. See also Using Dynamic Buffers.

  • Ports: BroPort for network ports, defined as follows:

    typedef struct bro_port {
        uint64       port_num;   /* port number in host byte order */
        int          port_proto; /* IPPROTO_xxx */
    } BroPort;
  • Records: BroRecord, kept opaque. See also Handling Records.

  • Strings (character and binary): BroString, defined as follows:

    typedef struct bro_string {
        uint32       str_len;
        uchar       *str_val;
    } BroString;
  • BroStrings are mostly kept transparent for convenience; please have a look at the Broccoli API Reference.

  • Tables: BroTable, kept opaque. See also Handling Tables.

  • Sets: BroSet, kept opaque. See also Handling Sets.

  • IP Address: BroAddr, defined as follows:

    typedef struct bro_addr {
      uint32      addr[4];   /* IP address in network byte order */
      int         size;      /* Number of 4-byte words occupied in addr */
    } BroAddr;

    Both IPv4 and IPv6 addresses are supported, with the former occupying only the first 4 bytes of the addr array.

  • Subnets: BroSubnet, defined as follows:

    typedef struct bro_subnet {
        BroAddr      sn_net;     /* IP address in network byte order */
        uint32       sn_width;   /* Length of prefix to consider. */
    } BroSubnet;

Managing Connections

You can use Broccoli to establish a connection to a remote Bro, or to create a Broccoli-enabled server application that other Bros will connect to (this means that in principle, you can also use Broccoli purely as middleware and have multiple Broccoli applications communicate directly).

In order to establish a connection to a remote Bro, you first obtain a connection handle. You then use this connection handle to request events, connect to the remote Bro, send events, etc. Connection handles are pointers to BroConn structures, which are kept opaque. Use bro_conn_new() or bro_conn_new_str() to obtain a handle, depending on what parameters are more convenient for you: the former accepts the IP address and port number as separate numerical arguments, the latter uses a single string to encode both, in “hostname:port” format.

To write a Broccoli-enabled server, you first need to implement the usual socket() / bind() / listen() / accept() routine. Once you have obtained a file descriptor for the new connection from accept(), you pass it to the third function that returns a BroConn handle, bro_conn_new_socket(). The rest of the connection handling then proceeds as in the client scenario.

All three calls accept additional flags for fine-tuning connection behaviour. These flags are:

  • BRO_CFLAG_NONE: no functionality. Use when no flags are desired.
  • BRO_CFLAG_RECONNECT: When using this option, Broccoli will attempt to reconnect to the peer transparently after losing connectivity. Essentially whenever you try to read from or write to the peer and its connection has broke down, a full reconnect including complete handshaking is attempted. You can check whether the connection to a peer is alive at any time using bro_conn_alive().
  • BRO_CFLAG_ALWAYS_QUEUE: When using this option, Broccoli will queue any events you send for later transmission when a connection is currently down. Without using this flag, any events you attempt to send while a connection is down get dropped on the floor. Note that Broccoli maintains a maximum queue size per connection so if you attempt to send lots of events while the connection is down, the oldest events may start to get dropped nonetheless. Again, you can check whether the connection is currently okay by using bro_conn_alive().
  • BRO_CFLAG_DONTCACHE: When using this option, Broccoli will ask the peer not to use caching on the objects it sends to us. This is the default, and the flag need not normally be used. It is kept to maintain backward compatibility.
  • BRO_CFLAG_CACHE: When using this option, Broccoli will ask the peer to use caching on the objects it sends to us. Caching is normally disabled.
  • BRO_CFLAG_YIELD: When using this option, bro_conn_process_input() processes at most one event at a time and then returns.

By obtaining a connection handle, you do not also establish a connection right away. This is done using bro_conn_connect(). The main reason for this is to allow you to subscribe to events (using bro_event_registry_add(), see Receiving Events) before establishing the connection. Upon returning from bro_conn_connect() you are guaranteed to receive all instances of the event types you have requested, while later on during the connection some time may elapse between the issuing of a request for events and the processing of that request at the remote end. Connections are established via TCP, optionally using SSL encryption. See “Configuring Encrypted Communication”, for more information on setting up encryption. The port numbers Bro agents and Broccoli applications listen on can vary from peer to peer.

Finally, bro_conn_delete() terminates a connection and releases all resources associated with it. You can create as many connections as you like, to one or more peers. You can obtain the file descriptor of a connection using bro_conn_get_fd():

char host_str[] = "";
int port        = 1234;
struct hostent *host;
BroConn *bc;

if (! (host = gethostbyname(host_str)) || !
    /* Error handling -- could not resolve host */

/* In this example, we obtain a connection handle, then register
event handlers, and finally connect to the remote Bro. */
/* First obtain a connection handle: */
if (! (bc = bro_conn_new((struct in_addr*) host->h_addr_list[0],
                         htons(port), BRO_CFLAG_NONE)))
    /* Error handling  - could not get connection handle */

/* Register event handlers: */
bro_event_registry_add(bc, "foo", bro_foo_handler, NULL);
/* ... */

/* Now connect to the peer: */
if (! bro_conn_connect(bc))
    /* Error handling - could not connect to remote Bro. */

/* Send and receive events ... */

/* Disconnect from Bro and clean up connection */

Or simply use the string-based version:

char host_str[] = "";
BroConn *bc;

/* In this example we don't request any events from the peer,
   but we ask it not to use the serialization cache. */
/* Again, first obtain a connection handle: */
if (! (bc = bro_conn_new_str(host_str, BRO_CFLAG_DONTCACHE)))
    /* Error handling  - could not get connection handle */

/* Now connect to the peer: */
if (! bro_conn_connect(bc))
    /* Error handling - could not connect to remote Bro. */

/* ... */

Connection Classes

When you want to establish connections from multiple Broccoli applications with different purposes, the peer needs a means to understand what kind of application each connection belongs to. The real meaning of “kind of application” here is “sets of event types to request”, because depending on the class of an application, the peer will likely want to receive different types of events.

Broccoli lets you set the class of a connection using bro_conn_set_class(). When using this feature, you need to call that function before issuing a bro_conn_connect() since the class of a connection is determined at connection startup:

if (! (bc = bro_conn_new_str(host_str, BRO_CFLAG_DONTCACHE)))
    /* Error handling  - could not get connection handle */

/* Set class of this connection: */
bro_conn_set_class(bc, "syslog");

if (! bro_conn_connect(bc))
    /* Error handling - could not connect to remote Bro. */

If your peer is a Bro node, you need to match the chosen connection class in the remote Bro’s Communication::nodes configuration. See Configuring event reception in Bro scripts, for how to do this. Finally, in order to obtain the class of a connection as indicated by the remote side, use bro_conn_get_peer_class().

Composing and sending events

In order to send an event to the remote Bro agent, you first create an empty event structure with the name of the event, then add parameters to pass to the event handler at the remote agent, and then send off the event.

Let’s assume we want to request a report of all connections a remote Bro currently keeps state for that match a given destination port and host name and that have amassed more than a certain number of bytes. The idea is to send an event to the remote Bro that contains the query, identifiable through a request ID, and have the remote Bro answer us with remote_conn events containing the information we asked for. The definition of our requesting event could look as follows in the Bro policy:

event report_conns(req_id: int, dest_host: string,
                   dest_port: port, min_size: count);

First, create a new event:

BroEvent *ev;

if (! (ev = bro_event_new("report_conns")))
    /* Error handling - could not allocate new event. */

Now we need to add parameters to the event. The sequence and types must match the event handler declaration – check the Bro policy to make sure they match. The function to use for adding parameter values is bro_event_add_val(). All values are passed as pointer arguments and are copied internally, so the object you’re pointing to stays unmodified at all times. You clean up what you allocate. In order to indicate the type of the value passed into the function, you need to pass a numerical type identifier along as well. Table-1 lists the value types that Broccoli supports along with the type identifier and data structures to point to.

Types, type tags, and data structures for event parameters in Broccoli
Type Type tag Data type pointed to
Boolean BRO_TYPE_BOOL int
Integer value BRO_TYPE_INT uint64
Counter (nonnegative integers) BRO_TYPE_COUNT uint64
Enums (enumerated values) BRO_TYPE_ENUM uint64 (see also description of bro_event_add_val()’s type_name argument)
Floating-point number BRO_TYPE_DOUBLE double
Timestamp BRO_TYPE_TIME double (see also bro_util_timeval_to_double() and bro_util_current_time())
Time interval BRO_TYPE_INTERVAL double
Strings (text and binary) BRO_TYPE_STRING BroString (see also family of bro_string_xxx() functions)
Network ports BRO_TYPE_PORT BroPort, with the port number in host byte order
IPv4/IPv6 address BRO_TYPE_IPADDR BroAddr, with the addr member in network byte order and size member indicating the address family and number of 4-byte words of addr that are occupied (1 for IPv4 and 4 for IPv6)
IPv4/IPv6 subnet BRO_TYPE_SUBNET BroSubnet, with the sn_net member in network byte order
Record BRO_TYPE_RECORD BroRecord (see also the family of bro_record_xxx() functions and their explanation below)
Table BRO_TYPE_TABLE BroTable (see also the family of bro_table_xxx() functions and their explanation below)
Set BRO_TYPE_SET BroSet (see also the family of bro_set_xxx() functions and their explanation below)

Knowing these, we can now compose a request_connections event:

BroString dest_host;
BroPort dest_port;
uint32 min_size;
int req_id = 0;

bro_event_add_val(ev, BRO_TYPE_INT, NULL, &req_id);

bro_string_set(&dest_host, "");
bro_event_add_val(ev, BRO_TYPE_STRING, NULL, &dest_host);

dest_port.port_num = 80;
dest_port.port_proto = IPPROTO_TCP;
bro_event_add_val(ev, BRO_TYPE_PORT, NULL, &dest_port);

min_size = 1000; bro_event_add_val(ev, BRO_TYPE_COUNT, NULL, &min_size);

The third argument to bro_event_add_val() lets you specify a specialization of the types listed in Table-1. This is generally not necessary except for one situation: when using BRO_TYPE_ENUM. You currently cannot define a Bro-level enum type in Broccoli, and thus when sending an enum value, you have to specify the type of the enum along with the value. For example, in order to add an instance of enum transport_proto defined in Bro’s init-bare.bro, you would use:

int transport_proto = 2;
/* ... */
bro_event_add_val(ev, BRO_TYPE_ENUM, "transport_proto", &transport_proto);

to get the equivalent of “udp” on the remote side. The same system is used to point out type names when calling bro_event_set_val(), bro_record_add_val(), bro_record_set_nth_val(), and bro_record_set_named_val().

All that’s left to do now is to send off the event. For this, use bro_event_send() and pass it the connection handle and the event. The function returns TRUE when the event could be sent right away or if it was queued for later delivery. FALSE is returned on error. If the event gets queued, this does not indicate an error – likely the connection was just not ready to send the event at this point. Whenever you call bro_event_send(), Broccoli attempts to send as much of an existing event queue as possible. Again, the event is copied internally to make it easier for you to send the same event repeatedly. You clean up what you allocate:

bro_event_send(bc, ev);

Two other functions may be useful to you: bro_event_queue_length() tells you how many events are currently queued, and bro_event_queue_flush() attempts to flush the current event queue and returns the number of events that do remain in the queue after the flush.


you do not normally need to call this function, queue flushing is attempted every time you send an event.

Receiving Events

Receiving events is a little more work because you need to

  1. tell Broccoli what to do when requested events arrive,
  2. let the remote Bro agent know that you would like to receive those events,
  3. find a spot in the code path suitable for extracting and processing arriving events.

Each of these steps is explained in the following sections.

Implementing event callbacks

When Broccoli receives an event, it tries to dispatch the event to callbacks registered for that event type. The place where callbacks get registered is called the callback registry. Any callbacks registered for the arriving event’s name are invoked with the parameters shipped with the event. There are two styles of argument passing to the event callbacks. Which one is better suited depends on your application.

Expanded Argument Passing

Each event argument is passed via a pointer to the callback. This makes best sense when you know the type of the event and of its arguments, because it provides you immediate access to arguments as when using a normal C function.

In order to register a callback with expanded argument passing, use bro_event_registry_add() and pass it the connection handle, the name of the event for which you register the callback, the callback itself that matches the signature of the BroEventFunc type, and any user data (or NULL) you want to see passed to the callback on each invocation. The callback’s type is defined rather generically as follows:

typedef void (*BroEventFunc) (BroConn *bc, void *user_data, ...);

It requires a connection handle as its first argument and a pointer to user-provided callback data as the second argument. Broccoli will pass the connection handle of the connection on which the event arrived through to the callback. BroEventFunc’s are variadic, because each callback you provide is directly invoked with pointers to the parameters of the event, in a format directly usable in C. All you need to know is what type to point to in order to receive the parameters in the right layout. Refer to Table-1 again for a summary of those types. Record types are more involved and are addressed in more detail in Handling Records.


Note that all parameters are passed to the callback as pointers, even elementary types such as int that would normally be passed directly. Also note that Broccoli manages the lifecycle of event parameters and therefore you do not have to clean them up inside the event handler.

Continuing our example, we will want to process the connection reports that contain the responses to our report_conns event. Let’s assume those look as follows:

event remote_conn(req_id: int, conn: connection);

The reply events contain the request ID so we can associate requests with replies, and a connection record (defined in init-bare.bro in Bro). (It’d be nicer to report all replies in a single event but we’ll ignore that for now.) For this event, our callback would look like this:

void remote_conn_cb(BroConn *bc, void *user_data, int *req_id,
                    BroRecord *conn);

Once more, you clean up what you allocate, and since you never allocated the space these arguments point to, you also don’t clean them up. Finally, we register the callback using bro_event_registry_add():

bro_event_registry_add(bc, "remote_conn", remote_conn_cb, NULL);

In this case we have no additional data to be passed into the callback, so we use NULL for the last argument. If you have multiple events you are interested in, register each one in this fashion.

Compact Argument Passing

This is designed for situations when you have to determine how to handle different types of events at runtime, for example when writing language bindings or when implementing generic event handlers for multiple event types. The callback is passed a connection handle and the user data as above but is only passed one additional pointer, a BroEvMeta structure. This structure contains all metadata about the event, including its name, timestamp (in UTC) of creation, number of arguments, the arguments’ types (via type tags as listed in Table-1), and the arguments themselves.

In order to register a callback with compact argument passing, use bro_event_registry_add_compact() and pass it similar arguments as you’d use with bro_event_registry_add(). The callback’s type is defined as follows:

typedef void (*BroCompactEventFunc) (BroConn *bc, void *user_data,
                                     BroEvMeta *meta);


As before, Broccoli manages the lifecycle of event parameters. You do not have to clean up the BroEvMeta structure or any of its contents.

Below is sample code for extracting the arguments from the BroEvMeta structure, using our running example. This is still written with the assumption that we know the types of the arguments, but note that this is not a requirement for this style of callback:

void remote_conn_cb(BroConn *bc, void *user_data,
                    BroEvMeta *meta) {
    int *req_id; BroRecord *rec;

    /* For demonstration, print out the event's name: */

    printf("Handling a %s event.\n", meta->ev_name);

    /* Sanity-check the number of arguments: */

    if (meta->ev_numargs != 2)
        { /* error */ }

    /* Sanity-check the argument types: */

    if (meta->ev_args[0].arg_type != BRO_TYPE_INT)
        { /* error */ }

    if (meta->ev_args[1].arg_type != BRO_TYPE_RECORD)
        { /* error */ }

    req_id = (int *) meta->ev_args[0].arg_data;
    rec = (BroRecord *) meta->ev_args[1].arg_data;

    /* ... */

Finally, register the callback using bro_event_registry_add_compact():

bro_event_registry_add_compact(bc, "remote_conn", remote_conn_cb, NULL);
Requesting event delivery

At this point, Broccoli knows what to do with the requested events upon arrival. What’s left to do is to let the remote Bro know that you would like to receive the events for which you registered. If you haven’t yet called bro_conn_connect(), then there is nothing to do, since that function will request the registered events anyway. Once connected, you can still request events. To do so, call bro_event_registry_request():


This mechanism also implies that no unrequested events will be delivered to us (and if that happened for whatever reason, the event would simply be dropped on the floor).


At the moment you cannot unrequest events, nor can you request events based on predicates on the values of the events’ arguments.

Reading events from the connection handle

At this point the remote Bro will start sending you the requested events once they are triggered. What is left to do is to read the arriving events from the connection and trigger dispatching them to the registered callbacks.

If you are writing a new Bro-enabled application, this is easy, and you can choose among two approaches: polling explicitly via Broccoli’s API, or using select() on the file handle associated with a BroConn. The former case is particularly straightforward; all you need to do is call bro_conn_process_input(), which will go off and check if any events have arrived and if so, dispatch them accordingly. This function does not block – if no events have arrived, then the call will return immediately. For more fine-grained control over your I/O handling, you will probably want to use bro_conn_get_fd() to obtain the file descriptor of your connection and then incorporate that in your standard FD_SET/select() code. Once you have determined that data in fact are ready to be read from the obtained file descriptor, you can then try another bro_conn_process_input() this time knowing that it’ll find something to dispatch.

As a side note, if you don’t process arriving events frequently enough, then TCP’s flow control will start to slow down the sender until eventually events will queue up and be dropped at the sending end.

Handling Records

Broccoli supports record structures, i.e., types that pack a set of values together, placing each value into its own field. In Broccoli, the way you handle records is somewhat similar to events: after creating an empty record (of opaque type BroRecord), you can iteratively add fields and values to it. The main difference is that you must specify a field name with the value; each value in a record can be identified both by position (a numerical index starting from zero), and by field name. You can retrieve vals in a record by field index or field name. You can also reassign values. There is no explicit, IDL-style definition of record types. You define the type of a record implicitly by the sequence of field names and the sequence of the types of the values you put into the record.

Note that all fields in a record must be assigned before it can be shipped.

The API for record composition consists of bro_record_new(), bro_record_free(), bro_record_add_val(), bro_record_set_nth_val(), and bro_record_set_named_val().

On records that use field names, the names of individual fields can be extracted using bro_record_get_nth_name(). Extracting values from a record is done using bro_record_get_nth_val() and bro_record_get_named_val(). The former allows numerical indexing of the fields in the record, the latter provides name-based lookups. Both need to be passed the record you want to extract a value from, the index or name of the field, and either a pointer to an int holding a BRO_TYPE_xxx value (see again Table-1 for a summary of those types) or NULL. The pointer, if not NULL, serves two purposes: type checking and type retrieval. Type checking is performed if the value of the int upon calling the functions is not BRO_TYPE_UNKNOWN. The type tag of the requested record field then has to match the type tag stored in the int, otherwise NULL is returned. If the int stores BRO_TYPE_UNKNOWN upon calling, no type-checking is performed. In both cases, the actual type of the requested record field is returned in the int pointed to upon return from the function. Since you have no guarantees of the type of the value upon return if you pass NULL as the int pointer, this is a bad idea and either BRO_TYPE_UNKNOWN or another type value should always be used.

For example, you could extract the value of the record field “label”, which we assume should be a string, in the following ways:

BroRecord *rec = /* obtained somehow */
BroString *string;
int type;

/* --- Example 1 --- */

/* Use type-checking, will not accept other types */

if (! (string = bro_record_get_named_val(rec, "label", &type)))
    /* Error handling, either there's no field of that value or
       the value is not of BRO_TYPE_STRING. The actual type is now
       stored in "type". */

/* --- Example 2 --- */

/* No type checking, just report the existent type */

if (! (string = bro_record_get_named_val(rec, "label", &type)))
    /* Error handling, no field of that name exists. */

printf("The type of the value in field 'label' is %i\n", type);

/* --- Example 3 --- */

if (! (string = bro_record_get_named_val(rec, "label", NULL)))
    /* Error handling, no field of that name exists. */

/* We now have a value, but we can't really be sure of its type */

Record fields can be records, for example in the case of Bro’s standard connection record type. In this case, in order to get to a nested record, you use BRO_TYPE_RECORD:

void remote_conn_cb(BroConn *bc, int *req_id, BroRecord *conn)
    BroRecord *conn_id;
    int type = BRO_TYPE_RECORD;
    if ( ! (conn_id = bro_record_get_named_val(conn, "id", &type)))
        /* Error handling */

Handling Tables

Broccoli supports Bro-style tables, i.e., associative containers that map instances of a key type to an instance of a value type. A given key can only ever point to a single value. The key type can be composite, i.e., it may consist of an ordered sequence of different types, or it can be direct, i.e., consisting of a single type (such as an integer, a string, or a record).

The API for table manipulation consists of bro_table_new() bro_table_free(), bro_table_insert(), bro_table_find(), bro_table_get_size(), bro_table_get_types(), and bro_table_foreach().

Tables are handled similarly to records in that typing is determined dynamically by the initial key/value pair inserted. The resulting types can be obtained via bro_table_get_types(). Should the types not have been determined yet, BRO_TYPE_UNKNOWN will result. Also, as with records, values inserted into the table are copied internally, and the ones passed to the insertion functions remain unaffected.

In contrast to records, table entries can be iterated. By passing a function of signature BroTableCallback() and a pointer to data of your choosing, bro_table_foreach() will invoke the given function for each key/value pair stored in the table. Return TRUE to keep the iteration going, or FALSE to stop it.


The main thing to know about Broccoli’s tables is how to use composite key types. To avoid additional API calls, you may treat composite key types exactly as records, though you do not need to use field names when assigning elements to individual fields. So in order to insert a key/value pair, you create a record with the needed items assigned to its slots, and use this record as the key object. In order to differentiate composite index types from direct ones consisting of a single record, use BRO_TYPE_LIST as the type of the record, as opposed to BRO_TYPE_RECORD. Broccoli will then know to interpret the record as an ordered sequence of items making up a composite element, not a regular record.

brotable.c in the test/ subdirectory of the Broccoli tree contains an extensive example of using tables with composite as well as direct indexing types.

Handling Sets

Sets are essentially tables with void value types. The API for set manipulation consists of bro_set_new(), bro_set_free(), bro_set_insert(), bro_set_find(), bro_set_get_size(), bro_set_get_type(), and bro_set_foreach().

Associating data with connections

You will often find that you would like to connect data with a BroConn. Broccoli provides an API that lets you associate data items with a connection handle through a string-based key-value registry. The functions of interest are bro_conn_data_set(), bro_conn_data_get(), and bro_conn_data_del(). You need to provide a string identifier for a data item and can then use that string to register, look up, and remove the associated data item. Note that there is currently no mechanism to trigger a destructor function for registered data items when the Bro connection is terminated. You therefore need to make sure that all data items that you do not have pointers to via some other means are properly released before calling bro_disconnect().

Configuration Files

Imagine you have instrumented the mother of all server applications. Building it takes forever, and every now and then you need to change some of the parameters that your Broccoli code uses, such as the host names of the Bro agents to talk to. To allow you to do this quickly, Broccoli comes with support for configuration files. All you need to do is change the settings in the file and restart the application (we’re considering adding support for volatile configuration items that are read from the file every time they are requested).

A configuration is read from a single configuration file. This file can be read from different locations. Broccoli searches in this order for the config file:

  • The location specified by the BROCCOLI_CONFIG_FILE environment variable.
  • A per-user configuration file stored in ~/.broccoli.conf.
  • The system-wide configuration file. You can obtain the location of this config file by running broccoli-config --config.


BROCCOLI_CONFIG_FILE or ~/.broccoli.conf will only be used if it is a regular file, not executable, and neither group nor others have any permissions on the file. That is, the file’s permissions must look like -rw------- or -r--------.

In the configuration file, a # anywhere starts a comment that runs to the end of the line. Configuration items are specified as key-value pairs:

# This is the Broccoli system-wide configuration file.
# Entries are of the form <identifier> <value>, where the
# identifier is a sequence of letters, and value can be a string
# (including whitespace), and floating point or integer numbers.
# Comments start with a "#" and go to the end of the line. For
# boolean values, you may also use "yes", "on", "true", "no",
# "off", or "false".  Strings may contain whitespace, but need
# to be surrounded by double quotes '"'.
# Examples:
Foo/PortNum           123
Bar/SomeFloat         1.23443543
Bar/SomeLongStr       "Hello World"

You can also have multiple sections in your configuration. Your application can select a section as the current one, and queries for configuration settings will then only be answered with values specified in that section. A section is started by putting its name (no whitespace please) between square brackets. Configuration items positioned before the first section title are in the default domain and will be used by default:

# This section contains all settings for myapp.
[ myapp ]

You can name identifiers any way you like, but to keep things organized it is recommended to keep a namespace hierarchy similar to the file system. In the code, you can query configuration items using bro_conf_get_str(), bro_conf_get_int(), and bro_conf_get_dbl(). You can switch between sections using bro_conf_set_domain().

Using Dynamic Buffers

Broccoli provides an API for dynamically allocatable, growable, shrinkable, and consumable buffers with BroBuf. You may or may not find this useful – Broccoli mainly provides this feature in broccoli.h because these buffers are used internally anyway and because they are a typical case of something that people implement themselves over and over again, for example to collect a set of data before sending it through a file descriptor, etc.

The buffers work as follows. The structure implementing a buffer is called BroBuf, and is initialized to a default size when created via bro_buf_new() and released using bro_buf_free(). Each BroBuf has a content pointer that points to an arbitrary location between the start of the buffer and the first byte after the last byte currently used in the buffer (see buf_off in the illustration below). The content pointer can seek to arbitrary locations, and data can be copied from and into the buffer, adjusting the content pointer accordingly. You can repeatedly append data to the end of the buffer’s used contents using bro_buf_append().

<---------------- allocated buffer space ------------>
<======== used buffer space ========>                ^
^              ^                    ^                |
|              |                    |                |
buf            buf_ptr              buf_off          buf_len

Have a look at the following functions for the details: bro_buf_new(), bro_buf_free(), bro_buf_append(), bro_buf_consume(), bro_buf_reset(), bro_buf_get(), bro_buf_get_end(), bro_buf_get_size(), bro_buf_get_used_size(), bro_buf_ptr_get(), bro_buf_ptr_tell(), bro_buf_ptr_seek(), bro_buf_ptr_check(), and bro_buf_ptr_read().

Configuring Encrypted Communication

Encrypted communication between Bro peers takes place over an SSL connection in which both endpoints of the connection are authenticated. This requires at least some PKI in the form of a certificate authority (CA) which you use to issue and sign certificates for your Bro peers. To facilitate the SSL setup, each peer requires three documents: a certificate signed by the CA and containing the public key, the corresponding private key, and a copy of the CA’s certificate.

The OpenSSL command line tool openssl can be used to create all files necessary, but its unstructured arguments and poor documentation make it a pain to use and waste lots of people a lot of time [1]. For an alternative tool to create SSL certificates for secure Bro/Broccoli communication, see the create-cert tool available at

In order to enable encrypted communication for your Broccoli application, you need to put the CA certificate and the peer certificate in the /broccoli/ca_cert and /broccoli/host_cert keys, respectively, in the configuration file. Optionally, you can store the private key in a separate file specified by /broccoli/host_key. To quickly enable/disable a certificate configuration, the /broccoli/use_ssl key can be used.


This is where you configure whether to use encrypted or unencrypted connections.

If the /broccoli/use_ssl key is present and set to one of “yes”, “true”, “on”, or 1, then SSL will be used and an incorrect or missing certificate configuration will cause connection attempts to fail. If the key’s value is one of “no”, “false”, “off”, or 0, then in no case will SSL be used and connections will always be cleartext.

If the /broccoli/use_ssl key is not present, then SSL will be used if a certificate configuration is found, and invalid certificates will cause the connection to fail. If no certificates are configured, cleartext connections will be used.

In no case does an SSL-enabled setup ever fall back to a cleartext one.

/broccoli/use_ssl          yes
/broccoli/ca_cert          <path>/ca_cert.pem
/broccoli/host_cert        <path>/bro_cert.pem
/broccoli/host_key         <path>/bro_cert.key

In a Bro policy, you need to load the frameworks/communication/listen.bro script and redef Communication::listen_ssl=T, ssl_ca_certificate, and ssl_private_key, defined in init-bare.bro:

@load frameworks/communication/listen

redef Communication::listen_ssl=T;
redef ssl_ca_certificate   = "<path>/ca_cert.pem";
redef ssl_private_key      = "<path>/bro.pem";

By default, you will be prompted for the passphrase for the private key matching the public key in your agent’s certificate. Depending on your application’s user interface and deployment, this may be inappropriate. You can store the passphrase in the config file as well, using the following identifier:

/broccoli/host_pass        foobar


Make sure that access to your configuration is restricted.

If you provide the passphrase this way, it is obviously essential to have restrictive permissions on the configuration file. Broccoli partially enforces this. Please refer to the section on Configuration Files for details.

Configuring event reception in Bro scripts

Before a remote Bro will accept your connection and your events, it needs to have its policy configured accordingly:

  1. Load frameworks/communication/listen, and redef the boolean variable Communication::listen_ssl depending on whether you want to have encrypted or cleartext communication. Obviously, encrypting the event exchange is recommended and cleartext should only be used for early experimental setups. See below for details on how to set up encrypted communication via SSL.

  2. You need to find a port to use for the Bros and Broccoli applications that will listen for connections. Every such agent can use a different port, though default ports are provided in the Bro policies. To change the port the Bro agent will be listening on from its default, redefine the Communication::listen_port. Have a look at these policies as well as base/frameworks/communication/main.bro for the default values. Here is the policy for the unencrypted case:

    @load frameworks/communication/listen
    redef Communication::listen_port = 12345/tcp;

    Including the settings for the cryptographic files introduced in the previous section, here is the encrypted one:

    @load frameworks/communication/listen
    redef Communication::listen_ssl = T;
    redef Communication::listen_port = 12345/tcp;
    redef ssl_ca_certificate    = "<path>/ca_cert.pem";
    redef ssl_private_key       = "<path>/bro.pem";
  3. The policy controlling which peers a Bro agent will communicate with and how this communication will happen are defined in the Communication::nodes table defined in base/frameworks/communication/main.bro. This table contains entries of type Node, whose members mostly provide default values so you do not need to define everything. You need to come up with a tag for the connection under which it can be found in the table (a creative one would be “broccoli”), the IP address of the peer, the pattern of names of the events the Bro will accept from you, whether you want Bro to connect to your machine on startup or not, if so, a port to connect to (default is Communication::default_port also defined in base/frameworks/communication/main.bro), a retry timeout, whether to use SSL, and the class of a connection as set on the Broccoli side via bro_conn_set_class().

    An example could look as follows:

    redef Communication::nodes += {
        ["broping"] = [$host =, $class="broping",
                       $events = /ping/, $connect=F, $ssl=F]

    This example is taken from broping.bro, the policy the remote Bro must run when you want to use the broping tool explained in the section on test programs below. It will allow an agent on the local host to connect and send “ping” events. Our Bro will not attempt to connect, and incoming connections will be expected in cleartext.

Configuring Debugging Output

If your Broccoli installation was configured with --enable-debug, Broccoli will report two kinds of debugging information:

  1. function call traces and
  2. individual debugging messages.

Both are enabled by default, but can be adjusted in two ways.

  • In the configuration file: in the appropriate section of the configuration file, you can set the keys /broccoli/debug_messages and /broccoli/debug_calltrace to on/off to enable/disable the corresponding output.
  • In code: you can set the variables bro_debug_calltrace and bro_debug_messages to 1/0 at any time to enable/disable the corresponding output.

By default, debugging output is inactive (even with debug support compiled in). You need to enable it explicitly either in your code by assigning 1 to bro_debug_calltrace and bro_debug_messages or by enabling it in the configuration file.

Test programs

The Broccoli distribution comes with a few small test programs, located in the test/ directory of the tree. The most notable one is broping [2], a mini-version of ping. It sends “ping” events to a remote Bro agent, expecting “pong” events in return. It operates in two flavours: one uses atomic types for sending information across, and the other one uses records. The Bro agent you want to ping needs to run either the broping.bro or broping-record.bro policies. You can find these in the test/ directory of the source tree, and in <prefix>/share/broccoli in the installed version. broping.bro is shown below. By default, pinging a Bro on the same machine is configured. If you want your Bro to be pinged from another machine, you need to update the Communication::nodes variable accordingly:

@load frameworks/communication/listen;

global ping_log = open_log_file("ping");

redef Communication::nodes += {
    ["broping"] = [$host =, $events = /ping/,
                   $connect=F, $retry = 60 secs, $ssl=F]

event ping(src_time: time, seq: count) {
    event pong(src_time, current_time(), seq);

event pong(src_time: time, dst_time: time, seq: count) {
    print ping_log,
          fmt("ping received, seq %d, %f at src, %f at dest, one-way: %f",
              seq, src_time, dst_time, dst_time-src_time);

broping sends ping events to Bro. Bro accepts those because they are configured accordingly in the nodes table. As shown in the policy, ping events trigger pong events, and broccoli requests delivery of all pong events back to it. When running broping, you’ll see something like this:

> ./test/broping
pong event from seq=1, time=0.004700/1.010303 s
pong event from seq=2, time=0.053777/1.010266 s
pong event from seq=3, time=0.006435/1.010284 s
pong event from seq=4, time=0.020278/1.010319 s
pong event from seq=5, time=0.004563/1.010187 s
pong event from seq=6, time=0.005685/1.010393 s


[1]In other documents and books on OpenSSL you will find this expressed more politely, using terms such as “daunting to the uninitiated”, “challenging”, “complex”, “intimidating”.
[2]Pronunciation is said to be somewhere on the continuum between “brooping” and “burping”.

Broccoli API Reference

The API documentation describes Broccoli’s public C interface.

Copyright 2016, The Bro Project. Last updated on December 07, 2018. Created using Sphinx 1.8.2.